Don't allow interpolating SVGPaintKind::None.
Don't allow interpolating SVGPaintKind::None.

PR #18103 disallowed interpolation between fill:none and fill:none, but that change was regressed by the refactoring in PR #18239.
This patch restores the intended behavior, disabling animation of SVGPaintKind::None.

larsbergstrom/servo,paulrouget/servo,avadacatavra/servo,KiChjang/servo,mbrubeck/servo,notriddle/servo,cbrewster/servo,CJ8664/servo,eddyb/servo,saneyuki/servo,DominoTree/servo,fiji-flo/servo,saneyuki/servo,saneyuki/servo,szeged/servo,jimberlage/servo,mbrubeck/servo,larsbergstrom/servo,jimberlage/servo,upsuper/servo,anthgur/servo,DominoTree/servo,dsandeephegde/servo,KiChjang/servo,splav/servo,saneyuki/servo,paulrouget/servo,thiagopnts/servo,DominoTree/servo,pyfisch/servo,rnestler/servo,canaltinova/servo,dati91/servo,nnethercote/servo,mbrubeck/servo,mbrubeck/servo,paulrouget/servo,rnestler/servo,dsandeephegde/servo,dsandeephegde/servo,eddyb/servo,avadacatavra/servo,rnestler/servo,pyfisch/servo,jimberlage/servo,saneyuki/servo,jimberlage/servo,sadmansk/servo,CJ8664/servo,notriddle/servo,SimonSapin/servo,SimonSapin/servo,splav/servo,cbrewster/servo,CJ8664/servo,pyfisch/servo,mattnenterprise/servo,peterjoel/servo,szeged/servo,ConnorGBrewster/servo,DominoTree/servo,sadmansk/servo,peterjoel/servo,eddyb/servo,mbrubeck/servo,szeged/servo,canaltinova/servo,ConnorGBrewster/servo,SimonSapin/servo,szeged/servo,splav/servo,splav/servo,upsuper/servo,saneyuki/servo,upsuper/servo,ConnorGBrewster/servo,eddyb/servo,saneyuki/servo,thiagopnts/servo,peterjoel/servo,dati91/servo,jimberlage/servo,peterjoel/servo,pyfisch/servo,mattnenterprise/servo,mattnenterprise/servo,szeged/servo,thiagopnts/servo,szeged/servo,larsbergstrom/servo,larsbergstrom/servo,avadacatavra/servo,SimonSapin/servo,sadmansk/servo,larsbergstrom/servo,anthgur/servo,fiji-flo/servo,peterjoel/servo,jimberlage/servo,DominoTree/servo,ConnorGBrewster/servo,SimonSapin/servo,emilio/servo,ConnorGBrewster/servo,DominoTree/servo,canaltinova/servo,emilio/servo,eddyb/servo,KiChjang/servo,fiji-flo/servo,rnestler/servo,mattnenterprise/servo,eddyb/servo,dati91/servo,notriddle/servo,splav/servo,cbrewster/servo,notriddle/servo,nnethercote/servo,dati91/servo,larsbergstrom/servo,anthgur/servo,larsbergstrom/servo,nnethercote/servo,eddyb/servo,jimberlage/servo,thiagopnts/servo,larsbergstrom/servo,dati91/servo,mbrubeck/servo,rnestler/servo,KiChjang/servo,szeged/servo,nnethercote/servo,mattnenterprise/servo,avadacatavra/servo,canaltinova/servo,peterjoel/servo,anthgur/servo,rnestler/servo,CJ8664/servo,anthgur/servo,KiChjang/servo,szeged/servo,nnethercote/servo,KiChjang/servo,notriddle/servo,thiagopnts/servo,emilio/servo,ConnorGBrewster/servo,dsandeephegde/servo,mattnenterprise/servo,CJ8664/servo,SimonSapin/servo,fiji-flo/servo,eddyb/servo,pyfisch/servo,dsandeephegde/servo,avadacatavra/servo,sadmansk/servo,avadacatavra/servo,nnethercote/servo,canaltinova/servo,thiagopnts/servo,KiChjang/servo,fiji-flo/servo,szeged/servo,emilio/servo,emilio/servo,dati91/servo,upsuper/servo,fiji-flo/servo,paulrouget/servo,DominoTree/servo,saneyuki/servo,rnestler/servo,dsandeephegde/servo,jimberlage/servo,sadmansk/servo,thiagopnts/servo,pyfisch/servo,paulrouget/servo,canaltinova/servo,splav/servo,dati91/servo,dati91/servo,splav/servo,upsuper/servo,sadmansk/servo,nnethercote/servo,peterjoel/servo,notriddle/servo,ConnorGBrewster/servo,notriddle/servo,fiji-flo/servo,sadmansk/servo,pyfisch/servo,cbrewster/servo,splav/servo,upsuper/servo,CJ8664/servo,splav/servo,dsandeephegde/servo,upsuper/servo,anthgur/servo,cbrewster/servo,splav/servo,KiChjang/servo,cbrewster/servo,paulrouget/servo,canaltinova/servo,sadmansk/servo,mbrubeck/servo,notriddle/servo,anthgur/servo,paulrouget/servo,paulrouget/servo,DominoTree/servo,rnestler/servo,emilio/servo,larsbergstrom/servo,larsbergstrom/servo,saneyuki/servo,DominoTree/servo,upsuper/servo,peterjoel/servo,nnethercote/servo,fiji-flo/servo,emilio/servo,SimonSapin/servo,emilio/servo,nnethercote/servo,pyfisch/servo,paulrouget/servo,SimonSapin/servo,szeged/servo,canaltinova/servo,paulrouget/servo,KiChjang/servo,anthgur/servo,jimberlage/servo,pyfisch/servo,dsandeephegde/servo,emilio/servo,peterjoel/servo,notriddle/servo,mattnenterprise/servo,nnethercote/servo,pyfisch/servo,avadacatavra/servo,CJ8664/servo,cbrewster/servo,KiChjang/servo,saneyuki/servo,DominoTree/servo,CJ8664/servo,emilio/servo,thiagopnts/servo,mattnenterprise/servo,ConnorGBrewster/servo,peterjoel/servo,mbrubeck/servo,cbrewster/servo,avadacatavra/servo,notriddle/servo